First off, welcome and good choice in bikes!!
Did he remove the AI (air injection)? This will cause a popping on deceleration. Also, if you are running a little lean, you can also get a little popping. The mixture screw can be turned out to help with this. About 3 turns usually, then incremental 1/4 turns. You would need a D tool for this, which can be found at
http://www.newspeedmaster.com/html/d_tool.html. Use Dinqua's site
http://www.dinqua.com/Triumph/carbs0.html for help locating te mixture screw. Good luck and welcome aboard!
